1. Field of the Invention
The present invention relates to an end-contact type thermal recording head suitably used for printers, facsimile equipment and other recording devices, which use heat-sensitive recording media or thermally imaging ribbons, films or other intermediate media interposed between the recording head and the recording medium.
2. Discussion of the Prior Art
As a thermal recording head for a recording apparatus such as a printer and a facsimile receiver, there is known a side-contact type thermal head in which an integrated-circuit driver portion and an electrically resistive heat-generating portion are both disposed on the same side of a substrate, which corresponds to one of opposite major surfaces of the substrate. Also known is an end-contact type thermal head as disclosed in laid-open Publications 60-24965, 60-8081 and 61-40168 of unexamined Japanese Patent Applications. In the end-contact type thermal head, only the electrically resistive heat-generating portion is formed on one end face of the substrate.
In particular, the end-contact type thermal head is commonly used for various advantages over the side-contact type. These advantages include: better contact of the heat-generating portion with a heat-sensitive paper or thermal print ribbon or film; elimination of a relief portion required for the side-contact type, for avoiding a contact between the driver circuit and a platen of the recording apparatus; reduced size of the head; and easy formation of an end face having a high degree of flatness for the heat-generating portion.
For improving the quality of images recorded by the end-contact type thermal head, on the other hand, there is a need for minimizing a distance between recording electrodes and a return-circuit electrode or electrodes, which are electrically connected to electrically resistive films of the heat-generating portion. Further, the above distance should be uniform for all the recording electrodes. Since the recording and return-circuit electrodes are disposed on the opposite sides of the substrate, the thickness of the substrate should be reduced to meet the above need. However, a reduction of the substrate thickness to an extent sufficient to meet the need will lead to difficulty in handling or processing such a thin substrate, insufficient mechanical strength of the substrate, and other drawbacks. It is also recognized that the known end-contact type thermal head is not completely satisfactory in its contact characteristic or behavior and heat-generating response.
The known end-contact type thermal printing head has another drawback, which arises from its structural arrangement as shown in FIG. 38, in which the heat-generating portion 104 projects toward the heat-sensitive paper or thermal imaging ribbon or film, from a base member 108 on which is supported the thermal head assembly, is supported. Namely, the known end-contact type thermal head is generally incapable of rapidly or efficiently radiating the heat generated by the heat-generating portion, toward the base or other members of the printer, and accordingly suffers from blurring, blotting or expansion of recorded image dots, distortion of the image dots due to prolonged heat application from the heat-generating portion, and other drawbacks.
Further, the known end-contact type thermal head shown in FIG. 38 includes a glaze layer 106 formed on the end face of the substrate 102, so that the electrically resistive films of the heat-generating portion 104 are formed on the glaze layer 106. The glaze layer 106 is provided since it is difficult to obtain a sufficiently high surface finish quality of the end face. The glaze layer 106 assures improved thermal characteristic of the heat-generating portion 104, and is effective to reduce failure of electrical connection of the electrical resistive films of the heat-generating portion 104 to the recording and return-circuit electrodes 110 and 112. However, it is difficult to form the glaze layer 106 uniformly on the end face of the substrate 102. Further, there are limitations in the configurations of the substrate 102 and glaze layer 106 for obtaining desired thermal characteristic of the heat-generating portion 104. In other words, the freedom of design of the glaze layer 106 for the desired thermal characteristic of the heat-generating portion 104 is too low to attain the intended function of the glaze layer.
There is also proposed an end-contact type thermal recording head which uses a substrate having a thin-walled end portion on which the electrically resistive heat-generating portion is formed. This recording head has a problem of insufficient mechanical strength at the thin-walled end portion. This problem is serious particularly where the heat-generating portion is adapted to contact the heat-sensitive paper or thermally imaging film or ribbon under a comparatively high pressure.